I've had an ETRS since the late 1980s, it's been very reliable and of superb image quality with the standard 75mm lens.
Be aware that the shutter is interlocked by the film holder dark slide. And you cannot dry fire the shutter and advance the winder without film unless you flip down the little lever on the right side for multi-exposure.
You cannot release the film back with dark slide removed, another safety interlock.
There's a metal ring around the shutter button that turns in two positions, but it's been so long, I don't remember what it's for. Either shutter lock or mirror lockup. Best to get a PDF copy of the owner's manual from online.
I keep switching back and forth between WLF and prism finder. There's good reasons to use both, depending on subject matter and shooting style. I will also on occasion affix it to the top of a sturdy Bogen tripod and go hunting for landscape images, where it delivers the goods in spades.
There are available replacement ground glass view screens. Some have grids, while others just the center focusing spot. Kind of nice to have a few on hand. I like the grid for landscape and architecture, while for street I like the bare screen.
There's also a speed grip that works well with the prism finder. You pull the pin out and remove the film winder handle, then attach the base of the camera into the locking speed grip handle, whose film advance lever interlocks into where the film crank was attached. You have to double-stroke the speed grip lever to fully advance the film.
Having WLF, prism finder and speed grip gives you lots of combinations in camera handling. Really a great system, and prices are really nice now for the buyer.
I need to use it more in urban settings, thanks for posting this thread, as it might spur me on to action.
~Joe